A supercharging pressure control apparatus is known in the art, for example, as disclosed in Japanese Utility Model Publication No. S62-162349 (also referred to as Prior Art Publication 1), according to which supercharging pressure is controlled for an internal combustion engine having a turbocharger. The turbocharger supercharges intake air into the internal combustion engine.
According to the turbocharger of the above prior art (Prior Art Publication 1), as shown in FIG. 13, it is composed of a turbine housing 103 connected to an exhaust manifold 102 of an internal combustion engine 101, and a turbine wheel 104 arranged in a center of the turbine housing 103. The turbine housing 103 has a turbine scroll 105 extending from an inlet portion (through which exhaust gas is supplied into the turbine housing) to a wheel accommodating chamber, and a discharging pipe 106 extending from the wheel accommodating chamber to an outlet portion.
An inside of the turbine scroll 105 is divided by a partitioning wall 110 into two passage portions, that is, a first passage 111 and a second passage 112. A switching valve 113 is provided at an inlet portion of the second passage 112. During a low speed running operation, the inlet portion of the second passage 112 is closed by the switching valve 113 so that exhaust gas flows only through the first passage 111, while the switching valve 113 is opened during a high speed running operation in order that the exhaust gas flows through both of the first and second passages 111 and 112.
A waste-gate passage 115 is opened to the first passage 111, wherein the waste-gate passage 115 bypasses the turbine wheel 104 so that the exhaust gas bypasses the turbine wheel 104 and flows to the outlet portion of the discharging pipe 106. The waste-gate passage 115 is opened and/or closed by a waste-gate valve 116, so that the supercharging pressure is controlled at a value, which does not exceed a predetermined maximum supercharging pressure.
Another exhaust gas pressure control apparatus is further known in the art, for example, as disclosed in Japanese Patent Publication No. 2008-196332 (also referred to as Prior Art Publication 2), according to which exhaust gas pressure at an inlet portion of a turbocharger, that is, at an upstream side of a turbine wheel of the turbocharger, is controlled to be a value lower than a predetermined value.
According to the turbocharger of the above prior art (Prior Art Publication 2), as shown in FIG. 14, a turbine wheel 104 is accommodated in a wheel accommodating chamber of a turbine housing 103. A spiral turbine scroll 105 is formed at an outer periphery of the turbine wheel 104. Exhaust gas supplied from an engine (not shown) to an inlet portion of the turbine housing 103 is introduced into the turbine wheel 104 via the turbine scroll 105.
The turbine scroll 105 is divided by a partitioning wall 120 into two passages, namely, a first passage 121 and a second passage 122. At a branching out portion 123, at which the first and second passages 121 and 122 are branched out, a flow control valve 124 is provided for controlling flow amount of the exhaust gas flowing through the second passage 122.
A waste-gate passage 125 is connected to the second passage 122, so that the exhaust gas may bypass the turbine wheel 104. A waste-gate valve 126 is provided at a connecting portion between the second passage 122 and the waste-gate passage 125 so as to control the flow amount of the exhaust gas flowing through the waste-gate passage 125.
A further supercharging pressure control apparatus is known in the art, for example, as disclosed in Japanese Patent Publication No. H10-089081 (also referred to as Prior Art Publication 3), according to which supercharging pressure is controlled for an internal combustion engine having a variable capacitor type turbocharger. In the above turbocharger, an opening degree of a variable nozzle, which is provided at an inlet portion of a turbine rotor, is controlled. In addition, an opening degree of a waste-gate valve, which is provided in a bypass passage so that exhaust gas bypasses a turbine, is also controlled.
According to the supercharging pressure control apparatus of the above prior art (Prior Art Publication 3), as shown in FIGS. 15A to 15C, it has a waste-gate valve and a variable nozzle. It also has a single actuator 107 having an actuator rod 131, to which a driving shaft 132 for the variable nozzle as well as a driving shaft 133 for the waste-gate valve is respectively linked.
FIG. 15A shows a condition of a link structure between the actuator rod 131 and the driving shafts 132 and 133, when an engine rotational speed is in a low range.
FIG. 15B shows another condition of the link structure between the actuator rod 131 and the driving shafts 132 and 133, when the engine rotational speed is in a middle range.
FIG. 15C shows a further condition of the link structure between the actuator rod 131 and the driving shafts 132 and 133, when the engine rotational speed is in a high range.
A further supercharging pressure control apparatus is known in the art, for example, as disclosed in Japanese Patent Publication No. 2009-024584 (also referred to as Prior Art Publication 4), according to which supercharging pressure is controlled for an internal combustion engine having a twin-nozzle type turbocharger. In such a turbocharger, apart of exhaust gas is supplied to a first nozzle through a first passage, while another part of the exhaust gas is supplied to a second nozzle through a second passage.
According to the turbocharger of the above prior art (Prior Art Publication 4), as shown in FIG. 16, an inlet passage of a turbine housing 103 is divided by a partitioning wall 140 into a first passage 141 connected to a first nozzle portion and a second passage 142 connected to a second nozzle portion. A flow rate control valve 143 is provided in the turbine housing 103 for controlling flow amount of exhaust gas respectively flowing through the first and second passages 141 and 142. In addition, a bypass passage 145 and a waste-gate valve 146 are provided in the turbine housing 103, so that exhaust gas pressure may not be excessively increased.
An electromagnetic actuator 108, which is controlled by a control unit 147, drives the flow rate control valve 143 via a rod 149.
When a position of the flow rate control valve 143 is moved by the electromagnetic actuator 108 from a first position to a second position, a through-hole is opened so that the first and second passages 141 and 142 are communicated to each other.
When the position of the flow rate control valve 143 is moved by the electromagnetic actuator 108 from the second position to a third position, the waste-gate valve 146 is moved against a biasing force so that the bypass passage 145 is opened.
According to the above first prior art (Prior Art Publication 1), since the switching valve 113 and the waste-gate valve 116 are provided, it is necessary to provide actuators for respectively driving the switching valve 113 and the waste-gate valve 116. In other words, since it becomes necessary to provide two actuators, a structure of an exhaust pipe of the engine may become complicated and a cost is increased.
According to the above second prior art (Prior Art Publication 2), since the flow control valve 124 and the waste-gate valve 126 are provided, it is likewise necessary to respectively provide actuators for driving the flow control valve 124 and for driving the waste-gate valve 126. In the same manner to the first prior art, it is necessary to provide two actuators, and thereby a structure of an exhaust pipe of the engine may become complicated and a cost is increased.
According to the above third prior art (Prior Art Publication 3), there exists an idling stroke of the actuator rod 131 due to clearances, during which the driving shafts 132 and 133 for the variable nozzle and the waste-gate valve are not actually moved by the actuator rod 131. As a result, the opening degree of the variable nozzle or the waste-gate valve may not be stably controlled, and thereby control accuracy for the flow rate may be decreased and furthermore slapping sound may be generated when the link mechanism is changed from the idling stroke to a working stroke. In addition, it is necessary to provide biasing forces for respectively biasing the driving shafts 132 and 133 toward the actuator rod 131. As a result, an operational force of the actuator 107 for the actuator rod 131 may be increased.
According to the above fourth prior art (Prior Art Publication 4), there exists a clearance between the flow rate control valve 143 and the waste-gate valve 146, slapping sound may be generated when the flow rate control valve 143 is brought into contact with the waste-gate valve 146, or control accuracy for the flow amount may be decreased. Furthermore, it is necessary to provide a biasing force to the waste-gate valve 146 so that the waste-gate valve 146 is pushed toward the flow rate control valve 143. It is, therefore, a problem that an operational force of the electric actuator 108 is increased.
A turbocharger having two independent valves is known in the art, for example, as disclosed in the above Prior Art Publications 1 and 2 and so on.
The turbocharger disclosed in the above prior arts has a variable capacitor type valve (a valve for changing a cross sectional area of a passage, through which exhaust gas flows toward a turbine wheel) and a waste-gate valve.
An opening degree of the variable capacitor type valve is controlled depending on an engine rotational speed, an engine load (an opening degree of an acceleration pedal) and so on, so that a target torque is obtained depending on an operational condition of the engine.
The waste-gate valve prevents an over supercharging condition (an excessive increase of intake air pressure). An opening degree of the waste-gate valve is controlled depending on the supercharging pressure, exhaust gas pressure at an inlet of the turbine wheel and so on.
The variable capacitor type valve and the waste-gate valve are respectively operated depending on the different operating parameters.
According to the above prior arts (Prior Art Publications 1 and 2), two different actuators are provided so as to respectively and independently drive the variable capacitor type valve and the waste-gate valve. It is, therefore, a factor for increasing cost, size and weight of the turbocharger.
Therefore, there is a demand that both of the variable capacitor type valve and the waste-gate valve are operated by one actuator (for example, an electric actuator being composed of an electric motor and a reduction gear) in order to achieve a miniaturization, a decrease of weight, a cost-down of the apparatus.